The present invention relates to a charged particle beam application apparatus such as an electron microscope, an ion-beam machining/observation apparatus or the like.
In recent years, the integration densities of semiconductor products have been more and more enhanced, and higher definition of the circuit patterns is demanded. In the specimens on which circuit patterns are formed, typified by semiconductor wafers, various kinds of inspection means are used for the purpose of quality control and enhancement of yield. There are cited, for example, a scanning electron microscope (hereinafter, called a length measuring SEM) which irradiates charged particle beam to measure the dimensional accuracy of a circuit pattern, a scanning electron microscope (hereinafter, called a review SEM) which also irradiates charged particle beam to evaluate a defect of a circuit pattern or attached extraneous matters, and the like.
In the observation of a specimen typified by a wafer by using charged particle beam, the electric field distribution of the periphery of the specimen edge changes, and therefore, the image quality degradation such as distortion, or blur of the observation image of the above described periphery occurs. As the influence of this phenomenon, various problems are caused such as occurrence of an error to a measurement dimensional value, erroneous detection of a defect, and inability to obtain a clear image. As the means for solving the problems, there is proposed a method for controlling the electric field of the periphery of the edge to be uniform by adding a ring-shaped conductor element capable of applying a voltage to the specimen holding means in the vicinity of the specimen edge (see JP-A-2004-235149). Further, as another means, there is proposed a method for making the distribution of an electric field gentle by narrowing the height gap of the edge and the specimen holding means which has conventionally existed by surrounding the specimen by a specimen positioning component with substantially the same height as the specimen (see JP-A-2004-79516).
Depending on the specimen holding state, the observed image significantly differs. As an example of mechanical specimen holding, there is a method in which two reference pins are provided at the outer periphery of a specimen, and the specimen is held by the pressing force by a movable pin from the opposing direction. In this method, the holding force which increases the pressing force for the specimen increases, and a deviation of the specimen due to vibration can be reduced. However, the specimen is distorted on one hand, and observation with favorable accuracy becomes difficult. Further, since the wafer is thin, and the flatness is low (parallelism of the single body is favorable), the specimen tends to be held in the form of a concave shape or a convex shape. In such a state, the height significantly varies with the movement of the specimen (about 100 μm at the maximum), and therefore, the depth of focus or focus movable length of the electron-optical system has to be set to be large. This becomes a large constraint to the electronic lens design, and it becomes difficult to increase the resolution which leads to improvement in image quality. Thus, by using an electrostatic chuck for the specimen holding means, flattening of the specimen surface and reinforcement of the holding force can be achieved at the same time.